There were a number of questions that sprang to mind when I watched the video.

1. What did Ueshiba call this exercise?
Like "aiki age", "aiki sage", "asagao", etc, all those names actually meant something specific in training. Doesn't mean there is a name for this exercise. I was just curious.

2. Why isn't this exercise in modern training? If it is, where?
Some exercises were passed down. furitama, funekogi undo, tai no henko, etc. What happened to this one?

3. What other exercises didn't get passed along?
I'm sure there are some. What were they?

4. Why did Ueshiba pop off his feet in the first one, but then not do so again?
Did he just want to do something different for the first time to show the capability? Did he do it on accident, then realize the camera was rolling, and settle down?

5. How did Ueshiba pop off his feet?
My guess:
1: Structure. The body has to be rebuilt so that it works as one unit and there is little to no slack.
2: Intent. It has to be developed such that it can be used to rebuild the body.
3: Dantien. It must be developed such that it can freely move and has an expanded range of motion.
4. Use 1-3 together. Use intent to move dantien in a connected body in a specific manner.